(1) Field of the Invention
The present invention relates to a method of guiding an aircraft to a platform, and in particular a short-landing aircraft such as an aircraft having a rotary wing, for example.
The invention thus lies in the technical field of systems for assisting the piloting of an aircraft, and in particular automatic systems for providing rotorcraft with assistance in approaching platforms.
(2) Description of Related Art
A rotary wing aircraft must be capable of finding and approaching platforms and moving vessels in complete safety, independently of weather conditions and of visibility, and while avoiding any obstacles present in the approach zone.
The approach is carried out when taking account of the direction and the speed of the wind in the sector, of the type of platform being approached (stationary platforms, movable platforms, ships, or barges) of nearby obstacles (cranes, barges, platform-positioning boats, container ships, or super tankers sailing around the approach zone, or other nearby platforms), and of passenger comfort.
A platform approach is generally made up of the following flight segments.
An approach thus has an arrival segment connecting the last flight point of the current stage of flight with an initial approach point known as the initial approach fix (IAF). This arrival segment is generally positioned at an altitude of 1500 feet (ft), it being understood that a foot is a unit of length equal to 30.48 centimeters (cm).
An initial approach segment may connect the initial approach fix IAF to an intermediate point referred to as an intermediate fix (IF). This initial approach segment seeks to enable the aircraft to decelerate and to become aligned with the path that is to be followed.
An intermediate approach segment may connect the intermediate fix IF to a final approach point known as a final approach fix (FAF) to descend to an altitude of up to 1000 ft. The purpose of this segment is to bring the aircraft into alignment, to decelerate it, and to prepare for the final approach segment.
At least one final approach segment connects the final approach fix FAF to a decision point known as the missed approach point MAP.
By way of example, the final approach fix FAF is connected to the missed approach point MAP by passing via a leveling-off point LPO and an offset instrument point OIP.
If a pilot establishes visual contact with the platform at the decision point, the pilot can land the aircraft on the platform.
In contrast, an overshoot segment should be followed if visual contact with the platform is not achieved at this stage of the approach. This overshoot segment may also be followed at any time during the approach if the crew judges that to be appropriate. The purpose of this overshoot segment is to return to a safe altitude.
The final descent going from the final approach fix to the decision missed approach point MAP should be followed only in the absence of any obstacle in a corridor of 2 nautical miles (NM), where a nautical mile is a length of 1852 meters (m).
If obstacles are present in the corridor, then the approach procedure should be canceled on safety grounds. Detecting such obstacles can be difficult. The crew may have difficulty in evaluating whether the presence of a moving ship is such as to make it necessary to abort the approach procedure.
The following documents present known platform approach procedures:    the Document AC90-80B “Approval of off-shore standard approach procedures, airborne radar approaches, and helicopter en-route descent areas”, published Apr. 12, 1999;    the Document JAR OPS 3, Section 2, Subpart E IEM to Appendix 1 to JAR-OPS 3.430 subparagraph (d) (amendment 2, published Jan. 1, 2002);    the Document EU-OPS Commission Regulation (EU) No. 965/2012 of Oct. 5, 2012 (AMC1 CAT.OP MPA.120 and GM1 CAT.OP.MPA.120); and    the Document CAA paper 2010/01 “The SBAS off-shore approach procedure (SOAP”).
When weather conditions are unfavorable, an instrument approach is beneficial in terms of relieving the crew of stress, where the crew must pilot the aircraft manually in order to guide it to a zone where it is possible to obtain visual acquisition of the platform.
In the transition between a stage of flying by instruments and a stage of flying visually, the crew's attention needs to switch continuously between the display on the piloting screens of the instrument panel, and what can be seen outside in order to detect any visible sign or indication suitable for confirming the position of the platform (light, terrain). This way of approaching a platform is thus not entirely practical and can sometimes lead to errors of interpretation, e.g. in the event of fog leading to temporary loss of acquisition of the landing target.
Until now, instrument approaches to a platform or to a moving ship have been carried out without using a navigation computer, also known as a flight management system (FMS), and without coupling the autopilot of the aircraft on an approach path as predefined by the flight management system FMS.
Nowadays certain platforms are fitted with a device known as a non-directional beacon (NDB) that is used by the crew via the navigation computer as means for assisting navigation and for correlating the position of the aircraft with relative accuracy, but those means do not enable an approach flight plan to be prepared.
A navigation computer is known that is used to provide horizontal guidance while en route. For the approach stage, the crew determines an off-route target point corresponding to the coordinates of the platform to be reached as means for assisting in navigation. Nevertheless, the navigation computer does not segment the various stages of the approach to the platform so as to servo-control the autopilot on such guidance data (horizontal deflection, vertical deflection, speed setpoint).
The approach is then carried out manually or semi-manually with assistance from certain higher modes of the autopilot by using approach charts as published by the operators and as approved by the local authorities.
The weather radar of the aircraft may also be used as means for identifying the platform, and for detecting and avoiding any transient or stationary obstacle while approaching and during the final descent.
Document US 2010/0168939 proposes a module and an automated method of approaching a platform on an approach path constructed on the basis of approach points.
According to that Document US 2010/0168939, the pilot inputs into a module of the aircraft:
the coordinates of the target platform to be reached;
the final approach heading towards the platform;
an offset distance laterally separating the path to be followed from a path directed towards the platform along said approach heading; and
a descent height.
Under such circumstances, the module of the aircraft determines in particular the position of the initial approach fix IAF and of the final approach fix FAF in response to the data that has been input. The aircraft is then directed towards the initial approach fix.
In this way, the approach path as prepared includes a horizontal segment connecting the initial approach fix IAF to a final approach fix FAF.
Thereafter, the path has a descent segment followed by a level segment in order to connect the final approach fix FAF with a missed approach decision point MAP.
The initial approach fix IAF, the final approach fix FAF, and the missed approach decision point MAP are contained in a vertical plane parallel to the selected approach heading. It can be understood that the term “vertical plane” is used to designate a plane extending in the gravity direction with points in this vertical plane lying at various altitudes.
This vertical plane is offset relative to the platform by a distance equal to the input offset distance.
Document U.S. Pat. No. 7,016,772 B2 discloses a device for displaying information on vehicles as a function of the importance of the information (size, position, speed), and it discloses a system for a ship that combines radar information with information coming from an automatic identification system (AIS).
Document U.S. Pat. No. 8,296,001 B1 discloses a system for assisting a navigator by providing the characteristics of other vessels and by providing coastal information. A radar or an automatic identification system AIS may be used.
Document JP 3 763 004 B1 describes a system for protecting a descent plane for aircraft approaching an airport relative to ships with the help of an AIS.
The technological background also includes the following documents:    Esterline CMC Electronics, CMA-9000 flight management system operator's manual, operational program S/W 169-614873-022, publication No. 9000-GEN-0105, itel N), 930-6000088-00, Aug. 21, 2008;    N. McFarlane, “A new procedure for North Sea helicopter operations”, Second GIANT Use Forum, Brussels, Belgium, Oct. 9, 2008;    K. M. Dodson and J. R. A. Stevens, “A North Sea trial to investigate the use of differential GPS for instrument approaches to off-shore platforms”, paper presented at the 23rd European Rotorcraft Forum, Dresden, Germany, September 1997; and    Documents EP 2 249 126, GB 2 492 665, FR 2 943 778.